<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <script>
        var a = parseFloat(prompt('请输入第一个数字:'));
        var b = parseFloat(prompt('请输入第二个数字:'));
        var sum = a + b;
        alert('数字' + a + '加数字' + b + '的和是：' + sum);
    </script>
</body>

</html>